Torsional vibration dampers (TVDs) are commonly used to provide mechanical damping in physically large generator sets where a torque is applied to the rotatable shaft of an electrical machine by an external device (prime mover) such as a diesel engine or turbine, for example. Such TVDs are used to prevent the build up of dangerous torsional vibration levels in the rotatable shaft of the electrical machine during start-up, shut-down and the normal operation of the generator set.
A stand-alone TVD includes a primary member that is driven by an output shaft of the prime mover and a secondary member that applies a torque to the rotatable shaft of the electrical machine. The primary and secondary members are elastically connected together by suitable spring sets so that the torque that is applied to the primary member by the output shaft of the prime mover is transferred through the spring sets to the secondary member. Buffers are often provided within the TVD to restrict the relative rotational movement between the primary and secondary members and hence prevent overloading and excessive deflection of the spring sets. Such conventional stand-alone TVDs are physically large, expensive to manufacture and install and add significantly to the overall length of the generator set. They can also suffer from misalignment problems.
In the case where the stand-alone TVD is a viscous damper then damping chambers formed in the body of the secondary member are filled with a viscous working fluid, typically engine oil that is circulated from the prime mover. The damping chambers are connected together by narrow passageways. Relative rotational movement between the primary and secondary members of the TVD forces the viscous working fluid through the passageways between the damping chambers and past the ends of the spring sets (e.g. leaf springs) to dampen torsional vibrations. The engine oil has a high operating temperature (about 80° C.) and often contains contaminant particles that can cause blockages, increase wear and reduce the reliability of the TVD.